Abstract: Objective To explore progesterone-induced blocking factor (PIBF) expression in the placenta and blood of patients
with severe preeclampsia and its relationship with immune tolerance imbalance. Methods Forty-seven patients admitted
between January and December, 2012 were enrolled in this study, including 25 patients with early-onset severe preeclampsia
(EOPE) and 22 with late-onset severe preeclampsia (LOPE), with 25 women with normal pregnancy serving as control group.
The antenatal blood and postpartum placenta were collected for immunohistochemical staining to detect PIBF expression in
the placenta and for testing serum PIBF level using ELISA. Flow cytometry was used to detect the percentage of circulating
Th1 and Th2 cells and the Th1/Th2 ratio was calculated. Results PIBF was expressed in decidual cells, syncytiotrophoblasts
and partial cytotrophablasts. The serum PIBF levels were 213.58 ± 44.93 ng/ml in EOPE group, 243.00 ± 61.19 ng/ml in LOPE
group and 273.91±48.57 ng/ml in control group. There were significant differences in serum PIBF, blood Th1/Th2 and placenta
PIBF-IOD among the 3 groups (P<0.05). EOPE group had significantly lower serum PIBF, lower llacental PIBF quantity
(PIBF-IOD) and higher blood Th1/Th2 than the control group (P<0.05). Serum PIBF in women with severe preeclampsia was
positively correlated with placenta PIBF-IOD and negatively with blood Th1/Th2 ratio (P<0.05), but a negative correlation
between serum PIBF and 24-hour urinary protein was found only in EOPE group (P<0.05). Conclusion The immune tolerance
imbalance mediated by PIBF may participate in the pathogenesis of severe preeclampsia. PIBF, the immune suppressor
secreted by lymphocytes of pregnancy women, is also a protective factor against severe preeclampsia, which is expected to be
a new target in therapy.